1. Field of the Invention
The invention relates in general to a thin film transistor (TFT) substrate and method of manufacturing the same, and more particularly to a thin film transistor substrate capable of reducing the number of required photo masks and method of manufacturing the same.
2. Description of the Related Art
Thin film transistors have been largely applied in fabrication of liquid crystal displays. The typical process for manufacturing a thin film transistor substrate will be described in FIG. 1 to FIG. 5 as below.
Referring to FIG. 1, a cross-sectional view of a gate electrode formed on a substrate in the prior art is shown. A substrate 100 is provided first, and then a gate-electrode layer (not shown in FIG. 1) is deposited on the substrate 100. The gate-electrode layer is subsequently patterned by photolithography and etching to form a gate electrode 110.
Referring to FIG. 2, a cross-sectional view of the formation of a gate insulation layer, a semiconductor layer, and an ohmic contact layer on the substrate in the prior art is shown. After the gate electrode 110 is fabricated, a gate insulation layer 120 is formed on the substrate 100. Afterward a semiconductor layer 130 and an ohmic contact layer 140 are successively deposited on the gate insulation layer 120 and further etched by covering a patterned photoresist layer (not shown in FIG. 2) on the ohmic contact layer as a mask. Lastly, the patterned photoresist layer is removed as shown in FIG. 2.
Referring to FIG. 3, a cross-sectional view illustrating the formation of a drain electrode and a source electrode in the prior art is shown. A metal layer, deposited on the substrate 100, is patterned by photolithography and etching to form a drain electrode 160, a source electrode 165, and an opening above the gate electrode 110, which exposes the semiconductor layer 130.
Referring to FIG. 4, a cross-sectional view illustrating the formation of a passivation layer on the substrate in the prior art is shown. A passivation layer 170 is deposited on the substrate 100, and a contact hole in the passivation layer is formed to expose the drain electrode 160 by photolithography and etching.
Referring to FIG. 5, a cross-sectional view illustrating a transparent electrode layer in the prior art is shown. A transparent electrode layer 180 is deposited on the passivation layer 170 to fill the contact hole in the passivation layer 170. Similarly, the transparent electrode layer 180 is patterned by photolithography and etching to form a pixel electrode as shown in FIG. 5. The typical thin film transistor substrate fabrication as mentioned above requires a process using five photo masks as shown in FIG. 1 to FIG. 5 respectively, which can not satisfy the need for low cost.
In order to reduce the cost, a method of thin film transistor fabrication using only four photo masks has been developed, which is accomplished by combining two patterning processes in FIG. 2 and FIG. 3 to one photo-mask process. However, the thin film transistor substrate formed by using four photo masks gives rise to the problem that light emitted from the bottom of the substrate and provided for the liquid crystal display will illuminate the semiconductor layer to induce a photoelectric current, thereby worsening the “off” behavior of the thin film transistor and reducing the quality of the liquid crystal display.